JPS6055447B2 - How to recover uranium from wet phosphoric acid - Google Patents

Description

[Detailed description of the invention] The present invention recovers trace amounts of uranium contained in wet phosphoric acid obtained by decomposing phosphate rock with mineral acids such as sulfuric acid and phosphoric acid using gypsum as a medium. There is also information on methods.

Natural phosphate rock generally contains 100 to 200 ppm of uranium, and most of it is transferred to the phosphoric acid solution during the so-called wet phosphoric acid manufacturing process, in which this is wet-decomposed using a mixed acid of phosphoric acid and sulfuric acid. .

Although the concentration of uranium in the phosphoric acid solution is not very high,
Since the absolute amount of phosphoric acid solution produced is very large, attempts have been made to recover uranium from wet phosphoric acid. As industrial methods for recovering uranium from wet phosphoric acid, solvent extraction methods, ion exchange methods, precipitation methods, adsorption methods, etc. are known.

Solvent extraction is a method that is currently being industrialized worldwide, but it requires purification of phosphoric acid as a pretreatment to prevent sludge formation during the extraction process, and the equipment costs are high. Moreover, since the extraction solvent is expensive, complicated operations are required to avoid its loss. In addition to the need for pretreatment of phosphoric acid in the ion exchange method, the concentration of the phosphoric acid solution supplied to the ion exchange column must be operated at a lower concentration than the normally produced wet phosphoric acid. There are some problems with this method, and it has not yet been widely put into practical use. Precipitation and adsorption methods require further improvement because the uranium recovery agent is expensive and its loss is a problem. On the other hand, the present inventors have already developed a wet phosphoric acid production method in which phosphate rock is decomposed with sulfuric acid, which is characterized by allowing an oxidizing agent to coexist in the reaction step for producing gypsum to make the uranium in the solution hexavalent. Method for producing wet phosphoric acid with high uranium content (Japanese Unexamined Patent Publication No. 57-27911) Furthermore, adding hemihydrate phosphoric acid and/or a compound that produces hemihydrate phosphoric acid to the wet phosphoric acid, softening it to hemihydrate phosphoric acid, It is characterized by separating wet phosphoric acid and hemihydrate sulfur, hydrating the separated hemihydrate spar, then separating the hydrated spar, adding a precipitant to the separated liquid, and recovering uranium as an insoluble precipitate. A method for recovering uranium from wet phosphoric acid (Japanese Patent Application No. 56-2424), and an industrial recovery method related to improvement of the process of the latter invention (Japanese Patent Application No. 56-1624).
No. 77) was proposed.

The present invention achieves a method for recovering uranium from wet phosphoric acid, which achieves a high recovery rate with simple operations,
It is completed. Furthermore, JP-A No. 55-1444P discloses a solvent extraction method for uranium that is incorporated into the wet phosphoric acid production process using the hemihydrite method, taking advantage of the fact that tetravalent uranium is easily incorporated into hemihydrate. However, this method was a combination of a uranium recovery method and a phosphoric acid production method, and was applicable only to the phosphoric acid production process of the hemihydro-dihydromethod. Therefore, it cannot be applied to other wet phosphoric acid production methods such as the dihydrous method, anhydrous method, hemihydrous method, dihydric and hemihydrous method, and the uranium-containing liquid obtained by processing using gypsum as a medium is still large. In order to prevent the loss of P2O5 when extracting uranium from the liquid, it is necessary to use a limited method and conditions of solvent extraction, and the extraction solvent used in this solvent extraction method is expensive. However, equipment costs are high. The present invention eliminates the drawbacks of these conventional uranium recovery methods from phosphoric acid solutions, and uses phosphoric acid obtained by various wet phosphoric acid production methods (hereinafter referred to as wet phosphoric acid) or wet phosphoric acid with a SiO2 source and Add an alkaline source,
Sulfuric acid is added to phosphoric acid with a low fluorine content (hereinafter referred to as defluorinated phosphoric acid) in which fluorine in wet phosphoric acid is removed as an alkali silifluoride, and an alkali metal compound and hydrated gypsum are added to the resulting mixed acid. ．． After adding phosphate rock to form hemihydrate powder, preferably add at least an equivalent amount of phosphate rock to the sulfuric acid, perform wet decomposition to obtain hemihydrate powder, and then separate the hemihydrate powder to obtain the hemihydrate powder. Industrial recovery of uranium from wet phosphoric acid or defluorophosphoric acid, which is characterized by separating dihydrite from hydration of ko and adding a precipitant to the separated mother liquor to recover uranium as an insoluble precipitate. Regarding the method.

In this way, the method of the present invention separates the uranium recovery process and the phosphoric acid production process as completely separate processes, so it can be applied to wet phosphoric acid produced by any method, and uses gypsum as an extractant. The uranium recovery solution obtained by back-extracting with water does not contain components such as P2O5 and H2SO4, and uranium exists in a concentrated state, so uranium can be easily recovered by the precipitation method. The operation is also much simpler than the solvent extraction method.

On the other hand, in the method described in JP-A-55-14441@, when this precipitation method is applied, it has a negative effect on the phosphoric acid production process, and it is impossible to recover uranium by precipitation. The present invention will be explained in more detail below. In carrying out the present invention, in a wet phosphoric acid production method in which phosphate rock is separated with a mixed acid of sulfuric acid and phosphoric acid, an oxidizing agent is coexisted in the reaction step to produce gypsum to make the uranium in the solution hexavalent. Next, it is preferable to use wet phosphoric acid from which the generated gypsum is separated, or defluorinated phosphoric acid, which is obtained by further reducing the fluorine content in the wet phosphoric acid, as a raw material. Oxidizing agents include KClO3, NaClO3, H2O2, KMnO,, H
Examples include NO, hydrochloric acid, 02, and air.
The reason why defluorinated phosphoric acid is particularly preferred as a raw material is due to the fact that the fluorine content in phosphoric acid affects the uranium recovery rate, and the uranium recovery rate is higher when phosphoric acid with a lower fluorine content is used as a raw material. . If necessary, add more S to defluorophosphate.
Even better results can be obtained by adding an iO2 source and an alkali source to fix fluoride ions as silifluoride ions.
The reason for this correlation between fluorine content and uranium recovery rate is not clear, but it is thought that the presence of a large amount of fluorine ions may inhibit the substitution reaction between uranium and calcium to some extent. In this way, the smaller the amount of fluorine ions in phosphoric acid, the more effective it is for uranium recovery, but the limit is approximately 0.5%.
It has been experimentally shown that a high uranium recovery rate can be achieved if the amount is below. In addition, when applying gypsum to the raw material phosphoric acid, since tetravalent uranium is more easily incorporated into hemihydrate uranium than hexavalent uranium, methods such as adding a reducing agent such as metallic iron, electrolytic reduction, etc. It is desirable to reduce hexavalent uranium to tetravalent uranium. Next, sulfuric acid is added to the raw material phosphoric acid to form a mixed acid composition. The amount of sulfuric acid added is H2SO in the mixed acid.
The amount of 4 is up to 25 weight percent, preferably 5 to 15 weight percent. Next, an alkali metal compound is added and dissolved in the mixed acid to increase the concentration of alkali metal ions in the mixed acid.

The alkali metal compound is not particularly limited, but easily available Na compounds include NaOH, Na2cO3, N
aHCO, , NaCl. ．． NaNO, or KOH as a K compound. ．． K2SO4, K2CO3, KHCOJ
Either one of lKCl, KNO3, etc. may be added and dissolved. As for the amount of addition, it is preferable to increase the alkali metal ion concentration in the mixed acid by 0.1% or more, and although there is no particular upper limit on the upper limit, it is usually around 5%, and if it is more than that, it will not have a correspondingly significant effect. However, if it is less than 0.1%, the effect is small. A major feature of the present invention is that a high uranium recovery rate can be obtained simply by incorporating a simple step of adding and dissolving an alkali metal compound in a mixed acid. The reason for this correlation between alkali metal ion concentration and uranium yield is not clear, but it is thought that the presence of a large amount of alkali metal ions promotes the substitution reaction between uranium and calcium. Next, hydrated stone (dihydrate stone) is added to the mixed acid. Dihydrate works as a scavenger for uranium in the hemihydration process. It is preferable to reuse a part of the by-product dihydrate produced in the subsequent hydration process, but dihydrate produced from other processes is also effective. The amount added varies depending on the composition of the mixed acid, but it is generally added so that the slurry concentration in the hemihydration step is 5 to 5% by weight. In the next hemihydration step, the slurry of mixed acid and hydrated quartz is maintained at a temperature at which quartz dihydrate transforms to quartz hemihydrate. The transition temperature is about 85-90°C. The produced hemihydrate powder contains 10 ppm to 5000 ppm of uranium, but the mother liquor has a mixed acid composition containing 25% or less of sulfuric acid, and simply separating the hemihydrate powder as it is will not produce the product phosphoric acid. Therefore, in the next step, phosphate rock is added to the slurry containing the mixed acid and hemihydrate powder, and at the same time, the uranium in the phosphate rock is captured in the hemihydrate powder to react with excess sulfuric acid through a wet decomposition reaction. The amount of phosphate rock to be added is adjusted to match the H2SO4 concentration in the mixed acid, so that the mother liquor after the reaction has the composition of the product phosphoric acid. As with the hemihydration step, a reaction temperature of about 85 to 90°C is sufficient. After the added dihydrate and all the hemihydrate derived from phosphate rock are separated from the phosphoric acid, they are sent to the next uranium desorption step. After the back 7 desorption step, the above-mentioned prior invention (patent application 1982-
No. 24242). That is, the hemihydrate powder that has captured uranium is dispersed and hydrated in water, and in the process of transferring the hemihydrate powder to the dihydrate powder, uranium is expelled from the solid phase to the liquid phase side.

This operation is also a feature of the present invention, and the fact that the process of extracting uranium from hemihydrate quartz can be performed by a simple hydration operation is an advantage of using gypsum as a uranium recovery medium. It is. A trace amount of sulfuric acid, a hydration accelerator, or an oxidizing agent may be added to the hydration reaction to accelerate the reaction. The reaction can be carried out at room temperature. Dihydrate produced through hydration contains almost no uranium,
It is mechanically separated and removed from the hydrated mother liquor (hereinafter referred to as the recovered solution) in which uranium has been eluted. Operationally, the slurry concentration is preferably in the range of 5 to 4% by volume. Alternatively, the recovered liquid may be circulated to the hydration step to increase the uranium concentration in the recovered liquid. Through the above steps, uranium is separated from the phosphoric acid solution, and finally a recovered solution containing substantially no phosphoric acid is obtained in the form of a solution.

The recovered liquid is usually obtained from several tens of Ppm to several thousand Ppm as u, but when extracting uranium from the recovered liquid,
It can be easily and economically recovered by applying the precipitation method. Caustic soda, ammonium compounds and the like are commonly used as precipitants, but divalent iron salts, organic chelating reagents and the like are also used. Since phosphoric acid liquid, which is the raw material for recovered uranium, is the main product, no additives can be added that would reduce its value as a product, but the recovered liquid is no longer completely separated from the phosphoric acid manufacturing process. In addition to the above-mentioned precipitating agent, the liquid properties can be adjusted as desired by adding additives such as a flocculant, an adsorbent, a full-coat agent, a surfactant, and a pH regulator, so that uranium can be recovered effectively. On the other hand, it goes without saying that the recovered liquid, which does not contain harmful substances even if mixed with phosphoric acid, may be recycled to the phosphoric acid production process. In addition, a part of the separated hydrated gypsum can be recycled for use in the hemihydration process, and the rest can be discharged as is and used for cement, making it an extremely advantageous process from an industrial perspective. The present invention will be explained below with reference to Examples.

Examples 1 to 5 Wet phosphoric acid (P) obtained by decomposing Florida phosphate rock with sulfuric acid
2O5 concentration = 30%, F concentration = 1.5%, U concentration = 10
A mixed acid prepared by adding 30 g of 98% sulfuric acid to 300 g of 0 ppm) was placed in a polypropylene container equipped with a stirrer, and the mixture was immersed in an oil bath to reach 8 rC.

In order to reduce the uranium in the mixed acid to tetravalent uranium, 0.2 g of iron powder was added as a pretreatment while stirring. Each of the alkali metal compounds shown in Table 1 was added and dissolved in the pretreated mixed acid. Add 40 g of hydrated gypsum (U concentration = 2 ppm) to each of these mixed acids, adjust the slurry temperature to 87 ° C.
The reaction was allowed to proceed for 1 hour.

After confirming that the entire amount of hydrated quartz was transferred to hemihydrate quartz, we
．． 4%, U concentration 100 ppm) was added,
The slurry temperature was adjusted to 8rc and reacted for 2 hours. After confirming that the phosphate rock had reacted and turned into hemihydrate, it was filtered to obtain phosphoric acid. The hemihydrate cake was first soaked in hot water;
It was then washed with acetone and air dried. Table 1 shows the weight of the hemihydrate, the uranium content, and the uranium recovery rate in the hemihydrate process. Subsequently, the hemihydrate Kou NO. 60 g of 2 was dispersed and hydrated in 70 ml of water, filtered, and the washing water and mother liquor were combined to obtain 72 ml of recovered liquid.

The uranium concentration in the recovered liquid was 353 ppm1, so the uranium recovery rate in the hydration operation was 98%. Further PH
The recovered solution of 1 was neutralized to pH=5.5 using an aqueous NaOH solution to obtain 0.137 g of a precipitate such as sodium niuranate containing 18.5% (as U) of uranium. The uranium recovery rate for this operation was 99.9%. Therefore, NO. The overall uranium recovery rate for 2 was 94% (a). 96×0.98×
0.999). Similar hydration operation was performed on NO. l, 3,
Regarding 4 and 5 hemihydrate stones. As a result, the overall uranium recovery rate was NO. l=93%, NO. 3=9
5%, NO. 4,5=94%. Example 6 So-called defluorinated phosphoric acid ζ (P2O.
Concentration = 30%, F concentration = 0.5%, U concentration = 100pp
m) The same operations as in Examples 1 to 5 were performed on a mixed acid prepared by adding 30 g of 98% sulfuric acid to 300 g.

Pour into a polypropylene container with a stirrer and add 0.2 iron powder.
g was added for reduction treatment. Add 3 solid NaOH to the mixed acid.
．． 0g was added and dissolved. Next, 40 g of hydrated gypsum (U
Concentration = 2 ppm) was added, and the mixture was reacted for 1 hour at 8 rC with stirring. After confirming that the entire amount of hydrated quartz has been transferred to hemihydrate lithium, phosphate rock (BPL75 from Florida,
32 Da (34.4% P2O, 100 ppm U concentration) was added, and a decomposition reaction was carried out at 87°C for 2 hours. After confirming that it has become all hemihydrate, it is filtered, P2C) -, 30.9%
, 327 g of phosphoric acid containing 2 ppm of U was obtained.

The hemihydrate cake was washed first with hot water and then with acetone and air dried. The weight of the hemihydrate powder was 75 g, and the uranium content was 435 ppm as U. Therefore, the uranium recovery rate in the hemihydration operation was 98%. continue,
After dispersing and hydrating 60 g of the hemihydrate in 70 ml of water, it was filtered, and the washing water and mother liquor were combined to yield 72 ml of recovered liquid.
I got it. The uranium concentration in the recovered liquid was 355 ppm1, so the uranium recovery rate in the hydration operation was 98%. Furthermore, the recovered liquid with pH: 1 was neutralized with aqueous ammonia to pH=6, to obtain 0.134 g of ammonium uranate and other precipitates containing 19.0% (as U) of uranium. The uranium recovery rate for this operation was 99.9%. Therefore, the overall uranium recovery rate is 96% (0.98 x 0.98 x 0.999)
It was hot. Comparative Example 1 Wet phosphoric acid 30 same as Examples 1 to 5
Solid NaOH is added to the mixed acid of 0g and 30g of 98% sulfuric acid.
O. 3g was dissolved (the increased Na ion concentration was 0).
．． This corresponds to 0.05%.

) As a result of performing exactly the same operations as in Examples 1 to 5, the uranium recovery rate in the hemihydration step was 93%, the hydration step was 98%, the precipitation step was 99.9%, and the total uranium recovery rate was 93%. The recovery rate was 91% (0.93×0.98×0
．． 999).

Claims (1)

[Claims] 1 H_2SO obtained by adding sulfuric acid to wet phosphoric acid
＿4 Add dihydrate to a mixed acid containing 25% or less, hold it above the hemihydrate transition temperature to transform it to hemihydrate, then add phosphate rock and perform wet decomposition to produce the hemihydrate. In this method, uranium is recovered as an insoluble precipitate by separating the dihydrate obtained by separating the hemihydrate and hydrating the hemihydrate and adding a precipitant to the separated mother liquor. A method for recovering uranium from wet phosphoric acid, which is characterized by increasing the concentration of uranium to 1% or more and transferring dihydrate to hemihydrate. 2. The method according to claim 1, wherein the alkali metal ion is Na or K. 3. The method according to claims 1 and 2, in which defluorinated phosphoric acid containing 0.5% or less of F is used as the wet phosphoric acid. 4. The method according to claim 1, wherein a part of the separated dihydrate is returned to the mixed acid as a uranium recovery agent and used for circulation.